Tropical Cyclone Discussion
387 WTPZ42 KNHC 261434 TCDEP2 Tropical Storm Vance Discussion Number 21 NWS National Hurricane Center Miami FL EP222026 900 AM CST Mon Oct 26 2026 Vance is experiencing 15 to 20 kt of west-southwesterly vertical wind shear. It appears that the surface center is near the west-southwest edge of the main convective area. The latest TAFB Current Intensity number remains 3.5/55 kt. Recent objective intensity estimates from UW-CIMSS have been running in the 45-55 kt range. The initial intensity is held at 55 kt for this advisory. Vance's estimated motion is west-northwestward or 295/6 kt, aided by GPMI and AMSR-3 microwave passes from around 0800 UTC. This slow west-northwestward track is expected to continue over the next 24 hours or so due to a weak mid-level ridge to the north of the system. By Wednesday, a broad mid-level trough near the Baja California peninsula should induce a turn toward the north. The NHC track forecast has again been shifted to the west of the previous one, but not as far west as the Google DeepMind Ensemble Mean. The official forecast is in good agreement with the latest HFIP Corrected Consensus Approach (HCCA). Although Vance remains in a favorable thermodynamic environment with warm water and enough atmospheric moisture, the cyclone is experiencing moderate to strong west-southwesterly wind shear. The wind shear is forecast to increase a bit more (to near 25 kt) over the next 12 to 24 hours, and this should be enough to cause steady weakening over the next day or so. On Wednesday, as Vance turns northward and gets closer to the broad trough over Baja California and the subtropical jet, the west-southwesterly vertical wind shear increases to over 35 kt, and is forecast to increase further on Thursday. Surprisingly, most of the models hold onto this system as a tropical storm for a couple more days. The NHC forecast is slightly lower than the previous forecast, and lies in the middle of the guidance envelope through 48 hours, near the HCCA model. From 60 hours onward, the NHC intensity forecast is near the lower end of the model guidance suite, near the average of the GDMI and HCCA models. It is likely that Vance's convection will be sheared off by 72 hours, and the new forecast has moved up post-tropical timing to this period. Nearly all of the models show the circulation dissipating by day 5, so the NHC forecast shows dissipation by this time, just before it reaches the coast of Mexico. Key Messages: 1. Periods of heavy rainfall associated with Vance will impact portions of western Mexico during much of this week. This rainfall may produce flooding and mudslides across southern Sinaloa, southwest Durango and coastal sections of Nayarit, Jalisco, Colima and Michoacan, especially in areas along steep terrain. 2. Although the wind threat to southwest Mexico is decreasing as the forecast track shifts westward away from the coast, interests there should continue to monitor Vance's progress. FORECAST POSITIONS AND MAX WINDS INIT 26/1500Z 15.4N 105.7W 55 KT 65 MPH 12H 27/0000Z 15.7N 106.6W 45 KT 50 MPH 24H 27/1200Z 16.4N 107.6W 40 KT 45 MPH 36H 28/0000Z 17.6N 108.2W 40 KT 45 MPH 48H 28/1200Z 19.2N 108.4W 40 KT 45 MPH 60H 29/0000Z 20.7N 108.4W 35 KT 40 MPH 72H 29/1200Z 22.0N 108.2W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 30/1200Z 24.1N 108.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 31/1200Z...DISSIPATED